Controlling an underground object

ABSTRACT

In order to control the sonde of an underground object, such as an underground boring tool, a predetermined sequence of rotation steps is applied to the object and that sequence is detected. The detection of the appropriate sequence causes the sonde to change its function, for example by changing the carrier frequency of the signal transmitted by the sonde on to change the data output sequence or transfer rate, or to change output power. While it is possible to use a single rotation step, the use of more than one step, with each step to be carried out within a predetermined time, reduces the risk of error.

This application is a continuation of Ser. No. 10/601,189, filed Jun.23, 2003, now U.S. Pat. No. 6,980,123, which is a continuation of Ser.No. 09/504,833, filed Feb. 16, 2000, now U.S. Pat. No. 6,606,032, whichclaims priority to United Kingdom Application No. 9904010.7, filed Feb.22, 1999, the disclosures of which are incorporated herein by referencein their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the control of an underground object.It is particularly, but not exclusively, concerned with the control of asonde forming part of an underground boring tool.

2. Summary of the Prior Art

It is well known that if an underground boring tool generates a magneticfield, that magnetic field can be detected above ground by a suitablelocator. An example of this is described in e.g WO96/29615 in which asolenoid on or in the underground tool generates a magnetic field whichis detected to measuring locations. It is also possible, by modulatingthe magnetic field, to transmit information from the underground boringtool to the locator. Therefore, it is possible to have a sonde in whichsuch field generation, modulation, etc is controlled. The sonde thenmakes it possible to transmit information from the underground boringtool to the locator.

In particular, it is possible for the sonde to transmit datarepresenting the orientation of the underground boring tool. InWO96/29615, the boring tool incorporated a tilt sensor, and the sondecould then transmit the data from that sensor to the locator. Othersensors, such as roll sensors, may also be provided.

In such arrangements, the sonde generated a low frequencyelectromagnetic field (typically 8 to 30 kHz), which carrier ismodulated to transmit sensor data. Such communication is thus from thesonde to the locator, and there is no direct communication from thelocator to the sonde.

Normally, the carrier signal generated by the sonde is at apredetermined frequency. The locator is then controlled to detect thatcarrier frequency, and the modulations thereon. However, signallingbetween the sonde and the locator may be affected by interference fromunderground sources of electromagnetic radiation such as electricalcables, or the magnetic field distortion effects of buried metallicstructures. Such interference effects are frequency dependent, andtherefore it is possible that transmission between the sonde and thelocator at a particular frequency may be greatly affected by suchinterference, whereas transmission at another frequency may not beaffected, or affected much less. Of course, changing the carrierfrequency may also affect the range of transmission between the sondeand the locator, battery life, etc, and therefore there is potentially abalance between these factors. If the operator of the locator finds thatinterference is a problem, the operator may decide that operating atanother carrier frequency would be beneficial. However, in the existingsystems, it is not possible for the operator to signal to the sonde tochange frequency.

It would, of course, be possible to provide a suitable signalling pathfrom the locator to the sonde by increasing the complexity of both thelocator and the sonde. This would increase the size and cost of thesonde, which may not be desirable or practical for an underground boringtool.

However, existing underground boring tools are normally connected totheir drive in a way which permits the drive to rotate the boring tool.Many underground boring tools have an axially offset slanted face whichenables the boring tool to be steered so that it moves in the desireddirection at any time. In order to detect this rotation, sondesassociated with such tools include a roll sensor, information from whichcan be transmitted to the locator. In normal circumstances, theinformation from the roll sensor is used by the operator to control thedirection of movement of the boring tool.

SUMMARY OF THE INVENTION

However, it has been realised in accordance with the present inventionthat if a predetermined rotation or rotation sequence is applied to theunderground boring tool, a roll sensor can detect such rotation and therotation may be treated as a command for the sonde. Thus, if theoperator wants to signal to the sonde to change carrier frequency, apredetermined rotation or sequence of rotations is applied to theunderground or inaccessible boring tool, detected by the roll sensor ofthe sonde, which sonde then determines the frequency change needed.

Although the present invention has been formulated with particularapplication to an underground boring tool, it is applicable to ancontrol of an underground or inaccessible object in which apredetermined rotation or sequence of rotations is applied to thatobject, which rotations are treated as commands to signalling operationsfrom the underground object.

Where there is a single rotation, the present invention may provide thata change in carrier frequency of a sonde in the underground boring toolmay be triggered by a rotation which is different from that needed totrigger a change of the sonde to a state in which it does not generateelectromagnetic radiation (a “park” state). Alternatively, if the sondedoes not have such a park state, the change in frequency may betriggered by a single rotation.

It should be noted that the present invention is not limited to the casewhere the command triggers a change in carrier frequency but includesarrangements in which the command triggers other changes in functions ofthe sonde.

Preferably, a sequence of rotations is used to transmit a command, eachrotation of which must be completed within pre-set time limits. Thesequence is then chosen so that it will not occur during the normaloperation of the boring tool. The use of a time limit for each rotationin the sequence of rotations significantly reduce the probability of thedetection of a command during normal activities of the undergroundboring tool.

The present invention thus permits signalling to the sonde in anunderground boring tool without modification to the boring tool orsignificant alteration of the features or the physical size of thesonde. In addition to altering the carrier frequency of the sonde, otherfeatures of operation, such as data output sequence, data transfer rate,or carrier output power may be controlled by signalling using thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described in detail,by way of example, with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic block diagram of an embodiment of the presentinvention;

FIG. 2 shows the underground boring tool of FIG. 1 in more detail;

FIG. 3 is a block circuit diagram of the sonde of the boring tool ofFIG. 2; and

FIG. 4 is a block circuit diagram of the locator of the embodiment ofFIG. 1.

DETAILED DESCRIPTION

Referring first to FIG. 1, an underground boring tool 10 is driven froma drive means 11 via a drive shaft 12. The drive means is arranged tomove the boring tool 10 forward, but also to impart rotations to theboring tool 10. The boring tool 10 has a slanted leading face 13, andthus the orientation of the boring tool 10 affects the direction inwhich it will move.

The boring tool 10 contains a sonde 20, which incorporates a roll sensorwhich can detect the axial orientation of the boring tool 10. The sondealso includes means for generating a magnetic field, which generatingmeans is controllable so that the magnetic field has a carrier frequencyand a modulation means, thus the frequency may be modulated to transmitdata from the sonde 20. That magnetic field is detected by a suitablelocator 30. That locator 30 has means for signalling to a remote station40, which remote station is connected to the drive means 11. It is thuspossible for the operator of the locator 30 to control the movement ofthe underground boring tool 10 from the location of the locator, bysignalling to the remote station 40, which then controls the drive meansto drive the underground boring tool 10 in a suitable direction.

The sonde 20 is normally battery-driven and therefore to extend thetotal number of hours the sonde 20 underground, it may have a powersaving mode for times in which the sonde 20 is not required to transmitdata. This is known as the “park” mode. In that park mode, the sondeturns off the electromagnetic transmission, and also any other circuitsof the sonde 20 which are not used. In order to initiate the park mode,the boring tool 10 is rotated through a predetermined roll angle, whichcan be detected by the tilt sensor of the sonde 20. When the roll sensordetects that such a rotation has occurred, and there has been nosubsequent rotation for a suitable period such as 2 or 3 minutes, thesonde enters the park mode. When the sonde detects that predeterminedrotation, it may trigger a display on the remote station 40 to indicateto the operator that it has received the command to change to the parkmode after the predetermined delay, so that the operator can initiateanother rotation if the park mode is not needed. The park mode iscancelled immediately a further rotation of the underground boring toolis detected by the sonde 20.

FIG. 2 shows the underground boring tool 10 in more detail. The slantedleading face 13 is more clearly shown, and FIG. 2 also shows that theboring tool 10 has a slot 21 therein to aid the radiation ofelectromagnetic signals from the sonde 20. The sonde 20 is rotationallykeyed to the rest of the boring tool 10 by a key 22.

In accordance with the present invention, the underground boring tool isrotated through a predetermined angle a plurality of times. Thatpredetermined angle may be the same as that needed to initiate the parkmode, but this is not a problem provided the time interval betweensuccessive rotations is less than that needed to trigger the park modeitself.

If there are n steps in the sequence, the number of possible commands tothe sonde 20, in addition to the park command, is n−1. If the angle ofsuccessive rotations in the sequence is different from that needed totrigger the park mode, there would then be n possible commands, but itis convenient for the angles to be the same.

In such an arrangement, each rotation in the sequence must be completedwithin a suitable time, such as 60 s otherwise the command will not berecognised. This use of a time limit for each step to be completedsignificantly reduces the probability of a command being identifiedduring normal activities of the underground boring tool 10.

The ability to send commands to the sonde 20 by rotating the boring tool10 in a suitable sequence of rotations permits an operator to change theoperation of the sonde. For example, signalling between the sonde 20 andthe locator 30 may be affected by conductors such as utility lines andpipes 50, 51 underground adjacent the boring tool 10. The interferencegenerated is often frequency dependent, and therefore a change incarrier frequency may reduce the interference of the signalling.Therefore, if the operator using the locator 30 finds that there isinterference, e.g because particular signals from the sonde 20 are notdetected, a signal may be generated via the remote station 40 to thedrive means 11 to generate a command by rotation of the undergroundboring tool which causes the sonde 20 to change its carrier frequency.The operator may then determine if the interference is reduced, and thenthe sonde 20 continues to operate at that new frequency. If there isstill interference, the operator may again trigger the sonde 20 tochange frequency by causing another command to be transmitted to thesonde 20 by rotation of the boring tool 10. Other commands may changedata output sequence, data transfer rate, or the output power of thecarrier signal.

FIG. 3 shows the electrical structure of the sonde 20 in more detail.The sonde 20 is powered by a battery pack 60, which provides the inputto a power supply module 61 which outputs regulated supplies for thecircuits of the sonde 20. The control of the sonde 20 is by amicroprocessor 62 which receives inputs from a battery sensor 63, apitch sensor 64, a roll sensor 65 and a temperature sensor 66. Theprocessor receives data representing the outputs of the sensor 63 to 66and generates two outputs. One output controls a modulation unit 67which encodes the data which the sonde 20 is to transmit, and the secondoutput from the microprocessor 62 controls an output signal clock 68which generates a carrier signal which is modulated by the output fromthe modulation unit 67 in an amplifier 69. The signal from themicroprocessor 62 to the output signal clock 68 determines the frequencyor frequencies which that clock outputs to the amplifier 69. Theamplifier 69 then controls a solenoid 70 to generate electromagneticsignals in which the carrier signal from the output clock 68 ismodulated by the output from the modulation unit 67.

In this embodiment, it is preferable for the sensors to operate stepwise and thus, as shown in FIG. 3, the battery sensor has four outputlevels, the pitch sensor determines the pitch plus or minus 45° in stepsof 0.1°, and the roll sensor determines rotations in 12 or 16 equalsectors. Thus, the roil sensor permits a sequence of rotations to bedetected, in order to send commands to the sonde 20 by rotating theboring tool 10 in a suitable sequence of rotations. If such a sequenceof rotations generates a command which is identified by themicroprocessor 62 as one involving change of the output frequency, asuitable change is applied to the output clock 68.

FIG. 4 then shows in more detail a possible structure for the locator30. The locator has a detection coil 80, the output of which is passedvia a pre-amplifier 81, a band pass filter 82, and an adjustable gainamplifier 83 to a mixer 84. The mixer 84 also receives an input from afrequency synthesiser 85, the frequency of which is selected by asuitable input from the remote station 40 in a way which corresponds tothe frequency of the carrier signal from the sonde 20. Additionally,when the sonde frequency is changed, the locator frequency synthesiser85 is also changed under control of the operator/computer so that thedata can be received at the new frequency. The output of the mixer 84 isthen passed via a band pass filter 86 and an automatic gain controlamplifier 87 to a demodulator 88. The demodulator 88 receives the signalfrom the automatic gain control amplifier 87 and passes it directly, andvia a band pass filter 89, to a mixer 90, the output of which passes viaa low pass filter 91 and a comparator 92, to output data representingthe data applied as a modulation to the carrier signal from the sonde20. That data output may then be passed back to the remote station 40.

1. A method of operating an underground or inaccessible object, said object including a sonde arranged to emit signals having a plurality of non-orientation-dependent characteristics, said method comprising the steps of: applying a predetermined rotation sequence involving at least one rotation step to said object; detecting, said rotation sequence; wherein said detection of said rotation sequence causes said sonde to change from the emission of a hint signal having a first non-orientation-dependent characteristic to the emission of a second signal having a second nonorientation-dependent characteristic.
 2. A method according to claim 1 wherein said first non-orientation-dependent characteristic and said second non-orientation-dependent characteristic of said signal are a first carrier frequency and a second carrier frequency respectively.
 3. A method according to claim 1 wherein said first non-orientation-dependent characteristic and said second non-orientation-dependent characteristic of said signal are a first data output sequence and a second data output sequence respectively.
 4. A method according to claim 1 wherein said first non-orientation-dependent characteristic and said second non-orientation-dependent characteristic of said signal are a first data transfer rate and a second data transfer rate respectively.
 5. A method according to claim 1 wherein said first non-orientation-dependent characteristic and said second non-orientation-dependent characteristic of said signal are a first output power and a second output power respectively.
 6. A method according to claim 1 wherein said rotation sequence comprises a plurality of steps is completed within a predetermined time limit.
 7. Apparatus for operating an underground or inaccessible object, said apparatus including: a sonde for emitting a plurality of signals having predetermined non-orientation-dependent characteristics of the underground or inaccessible object; rotation means for applying a predetermined rotation sequence involving at least one rotation step to said object; detection means for detecting said predetermined rotation sequence; and response means activated by said detection of said predetermined rotation sequence for causing said sonde to change from the emission of a first signal having a first non-orientation-dependent characteristic to the emission of a second signal being a second non-orientation dependent characteristic.
 8. Apparatus according to claim 7 wherein said object is an underground boring tool and said detection means is a roll sensor.
 9. A method of operating an underground or inaccessible object including a sonde, said object being connected to an operator triggered drive means, said method comprising the steps of: signaling from said drive means to said sonde, said signaling including the operator triggering said operator triggered drive means to apply a predetermined rotational sequence involving at least one rotation step to said object; detecting said rotation sequence, wherein said detection of said rotation sequence causes said sonde to change from a first signal modulation to a second signal modulation.
 10. A method according claim 9 wherein said rotation sequence-comprises a plurality of rotation steps.
 11. A method according to claim 10 wherein each rotation of said plurality of steps is completed within a predetermined time limit. 